As capacitors having high capacitance and low ESR (equivalent series resistance) used in various electronic devices, aluminum solid electrolytic capacitor and tantalum solid electrolytic capacitor are used.
A solid electrolytic capacitor consists of an aluminum foil having fine pores on its surface layer or a sintered body of tantalum powder having fine pores inside as one electrode (conductor), a dielectric layer formed on the surface layer of the electrode having pores, the other electrode (usually, a semiconductor layer) formed on the dielectric layer and an electrode layer laminated on said other electrode.
There is a conventional method for mass-production of such a capacitor on industrial scale, as follows. For the purpose of simultaneously forming on multiple conductors dielectric layers and then semiconductor layers respectively, a metal frame having multiple long metal plates placed at regular intervals thereon on each of which plates the multiple conductors oriented in the same direction are placed and connected at regular intervals is placed on a container containing a separately-prepared solution for chemical formation. After the conductors are immersed in the solution, current is applied at constant voltage by using the metal frame as anode and a metal plate immersed in the solution for chemical formation as cathode to thereby form dielectric layer. Subsequently, by placing the metal frame alternately on a container containing a separately prepared raw material solution for forming a semiconductor layer and on a container containing an oxidizing agent solution for oxidizing the raw material to form a semiconductor, the conductors are immersed in each of the solutions to thereby chemically laminate a semiconductor layer on the dielectric layer on each of the conductors. Also, Japanese Patent Application Laid-Open Nos. S64-32619 and H2-224314 disclose a method wherein after forming a dielectric layer on one conductor, the conductor is immersed in a container containing a solution for forming a semiconductor layer and current is applied by using as anode an outside electrode placed in the vicinity of the conductor and as cathode a metal plate in the solution for forming a semiconductor layer, to thereby electrochemically laminate a semiconductor layer on the dielectric layer.